This is a reference data set collected for validation of the monthly land cover maps at a 3m and at a 10m resolution produced in the WP5. The reference data set has been collected by using Geo-Wiki toolbox for visual interpretation of very high-resolution images, including Planet data and Google maps. The data set has been collected over 3 AOIs. Each reference sample site corresponds to a 30m-by-30m box and includes information about monthly land cover type over the period 2018-2020. Land cover legend is the same as in ESA WorldCover map at a 10m resolution (https://worldcover2021.esa.int/). Fields: "rowid" – unique row identifier; "sampleid" – unique sample site identifier in the Geo-Wiki database; "samplegroupid" – group id with values 257(Portugal), 258 (Belgium), 259(Sicily); "x_min","x_max","y_min","y_max" – bounding box coordinates of each sample site (30m x 30m), in WGS84 "X2018_1","X2018_2",…, "X2020_12" – dominant land cover class in each sample site in each month from January 2018 to December 2020; Land cover codes: 10 – Tree cover 20 - Shrubland 30 - Grassland 40 - Cropland 50 – Urban/built-up 60 - Bare/Sparse vegetation 80 - Water 90 - Wetland 110 - Burnt 120 – Not sure